The cytochalasins are a group of fungal metabolites which show extensive biological activity including (a) inhibition of cytokinesis, (b) cell enucleation, (c) interference with blood platelet aggregation, (d) effects on blood clot breakdown, (e) effects on release of growth hormones, (f) anti-edemic activity, (g) antibiotic activity, (h) antitumor activity, (i) inhibition of the immune response. Although these compounds are not yet used in human chemotherapy, it is quite possible that cytochalasins, or related compounds, will eventually find practical application in medicine, particularly in transplant surgery or in treatment of hyperallergic diseases. Described as exemplary of the work to be done in this area are total synthesis of cytochalasin A and of proxiphomin. We expect that this synthetic work will be more precisely define the chemistry of these compounds and will provide needed information on structure-activity relationships within this class of natural products.